Method of making metallic arsenates.



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THOMAS A. MITCHELL, 0F READING, MASSACHUSETTS, ASSIGNOR T0 MEIMAC CHEMICAL, COMPANY, OF NORTH WOBURN, MASSACHUSETTS, A COJREORATION OF MASSACHUSETTS.

METHOD OF MAKING METALLIC ARSENATES.

No Drawing.

To all whom it may concern.

Be it known that I, THOMAS A. MITCHELL,

a citizen of the United States, residing at Reading, in'the county of Middlesex and State of Massachusetts, have invented certain new and useful Improvements in Methods of Making Metallic Arsenates, of which the following is a specification. This invention relates to a. novel method whereby arsenates of lead, or other metallic arsenates, may be prepared directly and in a single operation from the corresponding metals.

The present commercial rocesses of making arsenate of lead utillze litharge as a source of lead, in conjunction with either sodium arsenate or arsenic acid. Inasmuch as the litharge must be prepared frommetallic lead by a preliminary operation, it is obvious that a method which yields the arsenate directly from metallic lead, and without any expenditure of power for the electrolysis of solutions, represents a material industrial advance.

According to the present invention, arsenate of lead may be prepared directly from metallic lead, white arsenic (arsenic trioxid) and nitric acid. An example of a preferred procedure is as follows :--25 kilos of white arsenic and kilos of metallic lead are placed in a covered stoneware vessel,

from which a pipe leads to an absorber for recovering the oxide of nitrogen evolved during thev rocess. To this charge is added slowly, pre erably with stirrin 25 kilos of commercial nitric acid of 40[ aum." The temperature tends to rise as the reaction proceeds, but it is not permitted to go above 90 (1., being controlled either by limiting the rate of inflow of the acid or by suitably cooling the contents of-the vessel. As soon as the acid has all been admitted and the temperature within the vessel begins to fall, steam is introduced to maintain the temperature and complete the reaction. At the close of the operation the liquid contents of the vessel are drawn ofi, and the lead arsenate is collected on filters and washed. In the course of this process, nitric acid reacts with arsenic trioxid, forming arsenic acid, and being itself reduced to oxids of nitrogen. These gaseous oxids are reoxidized in the absorbing system in contact with water and iii-presence of an excess of air or oxy Specification of Letters Patent.

Patented May 116, 193%.

Application filed July at, 1915. Serial No. 41,497.

gen; and inasmuch as this reoxidation is practically quantitative, there is analmost undergoing further oxidation to arsenate in. presence of the nitric acid. In this manner, there results at the close of the reaction a commercially pure arsenate of lead. It has been found advisable to introduce the nitric acid slowly, as above described, in order to maintain practical control of the reaction at all times and to secure a complete absorption and recovery of the oxids of nitrogen.

It has been found that when the reaction is roperly conducted there is substantially no ormation of N 0, the production of which would involve a corresponding loss of nitro-' gen.

The spent liquors from the process contain small quantities of nitric acid and lead nitrate, and'are essentially similar in com positionto the spent liquors obtained in the direct preparatlon of lead arsenate from metallic lead and arsenic acid, as described in my copending application Serial No. 1,498, filed July 23, 1915, and they may if desired be. employed in conjunction with the said process. j

The present method is highly advantageous in practice, inasmuch as it utilizesmetallic lead Without necessity for first converting it into litharge; and also utilizes arsenic trioxid, the oxidation of which takes place in the same container and at the same time as the formation of the arsenate 0 lead.

entering into the constitution of the arse- 'trioxid to oxidation by the agency of nitric nate. acid in presence of metallic lead. 10

2. The method of making an arsenate of 'In testimony whereof I aflix-m'y signalead, Which consists in subjecting arsenic ture in presence of two Witnesses. 5 trioxid to oxidation in presence ofmetallic v THOMAS 'A. MITCHELL.

lead. Witnesses 3. The method of making an arsenate of RALPH R. GREENLEAF, lead, which consists in subjecting arsenic ALLEN M. DonenAss. 

